The mouse is a model system for studying mammalian development, and the identification of genes required during embryogenesis is essential in defining the underlying molecular mechanisms. A deletion allele encompassing the mouse piebald locus has defined a region associated with prenatal lethality, termed s1Acrg. Mutant embryos fail to close the cranial folds of the neural tube and midline structures are also malformed. The s1Acrg region has been mapped genetically and physically and has been cloned on two YACs; the region is estimated to be in the range of 500 Kb. The goal of this research project is to identify the gene(s) corresponding to the s1Acrg defect. The region is being covered with a contig of P1 clones that provide technical advantages over YACs. Exon trapping, cDNA selection and CpG island analysis will be used to identify expressed sequences from these clones. Candidate genes will be mapped and assayed by Northern blot and in situ hybridization for relevant temporal and spatial expression patterns. Candidate genes will also be assayed for their ability to rescue the mutant phenotype when introduced into transgenic mice. The s1Acrg defect will also be analyzed further by in situ hybridization using relevant molecular markers.